Wireless communications technologies have developed to a Long Term Evolution (LTE) system. To better improve a data rate of user equipment (UE), the LTE system can support a carrier aggregation (CA) technology. The CA technology mainly means configuring multiple carriers for one UE, to improve a data rate of the UE. A base station using the CA technology synchronously transmits data or a control signal on the multiple carriers. Correspondingly, the UE detects a physical downlink control channel (PDCCH) of each carrier and a corresponding physical downlink shared channel (PDSCH), and receives data on a downlink data channel or sends data on an uplink data channel.
The base station that supports the CA technology synchronously transmits data on the multiple carriers. Therefore, correspondingly, the UE that supports the CA technology may simultaneously detect downlink data on multiple downlink carriers. Because the LTE system uses a hybrid automatic repeat request (HARQ) mechanism, the UE needs to simultaneously provide a HARQ feedback for the downlink data on the multiple downlink carriers. With reference to a hybrid automatic repeat request-acknowledgment (HARQ-ACK) feedback requirement in the HARQ mechanism, the UE needs to feed back, on one channel, HARQ-ACK information of the downlink data on the multiple downlink carriers. The HARQ-ACK information may include acknowledgement (ACK) information and negative acknowledgement (NACK) information, and may further include DTX information.
In another aspect, in order that the base station can schedule the UE on the multiple downlink carriers and transmit downlink data, the UE needs to feed back channel state information (CSI) of each carrier to the base station. CSI reporting is classified into periodic CSI reporting and a periodic CSI reporting. The periodic CSI reporting is usually implemented using a physical uplink control channel (PUCCH). The base station configures parameters of periodic CSI reporting for each downlink carrier using higher layer signaling. These parameters may include a reporting period, a reporting subframe offset, a used PUCCH resource, a reporting mode, and the like of periodic CSI. According to the reporting period, the reporting subframe offset, the used PUCCH resource, the reporting mode, and the like, of the periodic CSI that are configured for each carrier, the UE may determine a bit quantity and reported content of periodic CSI reporting performed in a reporting subframe for each carrier.
It can be learned that, for the multiple carriers, the UE may need to simultaneously feed back the HARQ-ACK information for the downlink data carried on these carriers and the periodic CSI of the carriers to the base station in one uplink subframe. The HARQ-ACK information and the periodic CSI may be collectively referred to as uplink control information (UCI).
The PUCCH has a relatively small capacity, and the HARQ-ACK information is more important than the periodic CSI. Therefore, when the HARQ-ACK information and the periodic CSI are transmitted simultaneously on a resource of the PUCCH, the UE needs to preferentially ensure performance of transmitting the HARQ-ACK information by the UE. In current carrier aggregation supporting five carriers, to ensure transmission performance of HARQ-ACK information, the UE can feed back periodic CSI of a maximum of one carrier in one uplink subframe. Apparently, the foregoing manner results in lack of periodic CSI of other carriers, and affects accuracy in scheduling the UE by the base station on the multiple carriers.
As the LTE technology further evolves, carrier aggregation of more carriers, for example, carrier aggregation of 32 carriers, may be introduced into the CA technology. In this case, if the UE can still feed back periodic CSI of a maximum of one carrier in one uplink subframe, accuracy in scheduling the UE by the base station on the multiple carriers is severely affected. Therefore, in this case, a higher-capacity PUCCH format needs to be introduced to send UCI information. Therefore, the UE needs to simultaneously transmit HARQ-ACK information and periodic CSI of the multiple carriers in one uplink subframe on a resource of the higher-capacity PUCCH format.
As described above, the HARQ-ACK information is more important than the periodic CSI. Therefore, when the HARQ-ACK information and multiple pieces of periodic CSI are transmitted simultaneously on the resource of the PUCCH, transmission performance of the HARQ-ACK information needs to be ensured. In this case, currently, there is still no specific implementation solution to ensure the transmission performance of the HARQ-ACK information and to send as much periodic CSI as possible.